Partially implantable hearing aid device

ABSTRACT

Partially implantable hearing device having easily replaceable components. Outer ear canal units contain the microphone, power source and electronics for receiving acoustic energy or sound waves and converting them into a responsive and variable magnetic field. Magnetic fields of magnets implanted onto bones in the ossicular chain in the ear interact with the variable magnetic field to cause the bones in the ossicular chain to vibrate in response to received sound waves. The variable magnetic field can be created directly via electrical signals or indirectly wherein intermediate radio frequency waves are transmitted and received between external and implanted components.

This is division of application Ser. No. 07/258,788 filed 10/17/88, nowU.S. Pat. No. 4,957,47 .

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to hearing devices and, inparticular, to implantable hearing devices.

2. Description of the Related Art

With the advent of the operating microscope in the 1950's a newly bornfield of otology and microsurgery emerged. The development oftympanoplasty and stapedectomy have led to the amelioration of manyvarieties of conductive hearing loss. Even some sensorineural hearinglosses have been successfully treated using microsurgical techniques.

Despite these surgical accomplishments, however, 20 million people inthe United States of America still suffer from various degrees ofhearing loss. While the vast majority of the people in this group arecandidates for conventional hearing aid use, in reality onlyapproximately 15 percent becomes users of an amplification device toovercome their hearing loss. Several factors, such as sound distortion,discomfort of fit, and cosmetic appearance are ostensibly to blame forthis low incidence of conventional hearing aid use.

Volta, in 1800, first introduced the concept of stimulating the ear byusing electricity. The carbon hearing aid first appeared about the turnof the century. Another landmark development was the vacuum tube hearingaid, introduced in the late 1930's, which, in time, was supplanted inthe 1950's by the transistor-operated systems. All conventional hearingaids now use transistors and integrated circuits to improve frequencyresponse, reduce size, lower harmonic distortion and increaseflexibility of fit as compared to their predecessors, yet perhaps not tothe ultimate satisfaction of each potential user.

The conventional hearing aid is composed of a microphone, an amplifier,a battery as a power source, and a speaker or earphone (commonlyreferred to as a receiver in the hearing aid industry). The implantablehearing device has the same basic components, except that the speaker isreplaced by a driving vibrating component, such as an electromagneticcoil or a piezoelectric system of bimorph design. Environmental soundenergy, as it passes through either device, is converted by themicrophone into an electrical signal which is routed to an amplifier. Inthe conventional hearing aid, the speaker transduces the amplifiedelectrical signals into acoustic energy, which is then transmitted tothe tympanic membrane and ossicular chain. In the implantable hearingdevice, the speaker is eliminated, being replaced by the vibratorycomponent which drives the ossicular chain.

Some investigators have directed their efforts to the needs of thehard-of-hearing patient, designing systems intended to circumvent manyof the problems of the conventional hearing aid. Rutschmann, et al, in1959, described auditory stimulation by the use of alternating magneticfields acting on permanent magnets fixed to the ear drum. In 1967,investigators at the University of Pittsburgh, Department of ElectricalEngineering, designed the first implantable hearing aid of this type. AU.S. Patent was granted but no further animal or human research has beenreported.

U.S. Pat. No. 3,209,081 to Ducote, et al. discloses a hearing aid inwhich a sound amplifier and transmitter unit, carried on the body of theuser, is used to transmit radio frequency signals to a remote receiverthat is implanted subcutaneously against the skull of the user in aconcealed position.

U.S. Pat. No. 3,346,704 to Mahoney discloses a hearing aid unit adaptedto be implanted within the mastoid antrum of the user. The unitcomprises a microphone, a battery, an amplifying system, and a speaker.A microphone tube extends from the microphone to a point beneath theskin and behind the ear of the user to transmit sound from theenvironment to the microphone, while a speaker tube extends from thespeaker through the mastoid antrum into the middle ear space behind theear drum to transmit the sound thereto.

Wingrove, U.S. Pat. No. 3,594,514, discloses an implantable hearing aidhaving a piezoelectric ceramic element mounted adjacent to the auditoryconductive system of the middle ear to impart vibration thereto.Electrical circuitry connected to the piezoelectric element provideselectrical signals representative of sound waves.

Goode's 1970 article on the state of the art in implantable hearing aidsrekindled interest in this approach and progress continued throughoutthe early 1970's through the work of Glorig, et al., Vernon, et al., andFredrickson, et al. who explored the feasibility of differentimplantable systems. Patent activity in that time frame includes U.S.Pat. No. 3,764,748 to Branch, et al; U.S. Pat. No. 3,870,832 toFredrickson, and U.S. Pat. No. 3,882,285 to Nunley, et al.

Branch, et al., supra, discloses several hearing aid configurations forimplantation within the middle ear cavity interiorly of the ear drum tothe ossicle bone chain. Auditory signals picked off the ear drum aresubsequently amplified and/or transmitted to natural and/or solid-statesound receiving mechanisms located on the oval window, the round window,or the promontory leading into the inner ear. The tensor tympani andstapedial muscles prevent loud sounds from damaging the inner ear.

Fredrickson, supra, employs an implanted coil and magnet in the earafter removal of the incus. The magnet is fastened to the head of thestapes and the coil, when energized by electrical signals from a soundtransducer, produces a magnetic field which interacts with the magneticfield of the magnet. This interaction of the two magnetic fields causesmovement of the stapes in the same manner as it is normally activated bythe incus.

Nunley, et al., supra, discloses an implantable hearing aid which isimplanted in a hollowed-out portion of the skull adjacent to the earcanal. A microphone part is connected to the ear canal which receivessound that enters the ear and transforms it into energies which aretransmitted via mechanical means to the movable portions of the middleear. In this fashion, a parallel sound path is provided which augmentsand supports the transmission of sound to improve hearing.

Advances in technology in the 1980's have spurred additional efforts.Suzuki, et al. and Yanagihara, et al. have published reports whichdescribe middle ear implants in animals and humans using a piezoelectricvibrator of bimorph design. Several of their patients have reported goodamplification and high fidelity of sound perception; indeed, the effortsof the Japanese group constitutes a major breakthrough in implantationdevices.

Tjellstrom, et al., in 1981, 1983 and 1985, developed another variationof an implantable device. This system used a bone conduction "hearingaid" anchored directly to the temporal bone by implantedosseo-integrated titanium screws which exit to the surfacepercutaneously. While the incidence of infection has been low in theimplanted subjects, the device has not been received altogetherenthusiastically by many patients, ostensibly due to its design. It ishelpful in patients with 45 dB or better bone condution. In 1985, Hough,et al. introduced a modification of the temporal bone stimulator forpatients with bone conduction thresholds of 25 dB hearing loss orbetter. In this device, the titanium bone conduction vibrator is screwedinto the temporal bone and no electronics are used except for a radiolink coils to transmit the electrical signal transcutaneously. Avibrating coil activates the screw implanted in the bone. An ear-leveland body-borne variant of this system have been presented to date.Although the body-borne system provides about 10 dB more gain than theear level device, it has been less accepted by patients than the earlevel device. See U.S. Pat. No. 4,606,329 to Hough for further details.Neither device (body-borne or ear level) has been quite as efficient asthe Tjellstrom implant, perhaps because they employ indirect couplingthrough radio frequency transmission rather than direct bone conductionstimulation. Revisions of the electronic design may very well improvethe efficiency of the bone conduction temporal bone stimulator of Hough,and since the device has U.S. Food and Drug Administration (FDA)approval, it should receive considerable clinical application in theUnited States and abroad. For a description of a particular type ofcoupling to a bone-anchored hearing aid, see U.S. Pat. No. 4,498,461 toHakansson.

In 1987, Hough et al. reported on a middle ear implantable hearingdevice using electromagnetic principles applied to humans undergoingmiddle ear surgery under local anesthesia. Although the device wasfunctional, its electrical power consumption was excessive.

Ko, Maniglia and Zhang also reported, in 1987, their experience with anelectromagnetic middle ear hearing aid using direct stimulation of thestapes. Goode, et al. have experimented with a piezoelectric system toproduce stapes vibration in fresh human temporal bones. Heide, et al. in1988 presented the advantages of an electromagnetic hearing aid in theear canal driving a magnet glued to the ear drum. Finally, Goode hasrecently reported encouraging results with another design in whichanother electromagnetic canal device similar in principle and designthat stimulates a samarium cobalt magnet glued to the ear drum. However,the magnet glued to the ear drum only stays in place temporarily, and abetter system is necessary.

Thus, while technological advances in the conventional hearing aidindustry have succeeded in miniaturizing the components and improvingthe efficiency and gain of these devices, there are still problems to besolved. Some of the drawbacks associated with the conventional hearingaid are: high internal noise, acoustic feedback, limited fidelity due tosound distortion and a limited frequency response range. Additionally,many hearing aid styles are considered to be cosmetically unattractive,overly conspicuous, or even uncomfortable if they employ a tightlyfitting earmold. As a consequence, a highly efficient, totally concealedconventional hearing aid is not yet available. Finally, the candidacy ofa given person for hearing aid use may also be restricted on medicalgrounds because of such problems as chronic middle ear infections,stenosis or atresia of the external auditory canal, or prior radicalmastoidectomy.

In theory, the attractiveness of an implantable hearing device lies inits ability to overcome many of the drawbacks mentioned above for theconventional hearing aid. However, if any implantable device is toprovide a viable alternative to the conventional hearing aid, the devicemust not only overcome many of these drawbacks but it must also minimizeall potential risk factors introduced by the surgical procedure. Itshould be made out of biocompatible materials and have the lowest riskpossible regarding middle ear or inner ear complications. Ideally, itstechnical design should be trouble-free for many years so that the needfor revision surgery is minimal. Finally, it should have the followingadvantages: (1) totally concealed cosmetically; (2) highly efficientpower consumption; (3) high sound fidelity; (4) broad, flat frequencyresponse; (5) minimal sound distortion; (6) elimination of ringingfeedback; (7) adequate acoustic gain; and (8) be flexible and versatileso as to be applicable to cases involving conductive as well assensorineural hearing loss, and to all age groups, especially thepediatric age group that would probably derive the greatest benefit fromsuch a device, because of many more years of potential use.

SUMMARY OF THE INVENTION

The present invention provides a new and novel semi-implantable hearingdevice which overcomes the drawbacks of prior art devices, achieves theaforesaid advantages, and minimizes the risk factors introduced by thesurgical procedure itself.

Accordingly, one aspect of the present invention is drawn to a totallyconcealed, partially implantable hearing device having a replaceableouter ear canal unit and an implanted magnet attached to the malleusbone of the ear. The replaceable ear canal unit receives acoustic energyor sound waves that enter the ear and travel down the outer ear canal tothe unit. A microphone detects the sound waves and, with the help of abattery and an electronic amplifier, transforms the sound waves intoamplified electrical signals. The electrical signals activate anelectromagnetic driving coil, i.e., a coil of wire wrapped around aferrite alloy core, which creates a magnetic field that varies inresponse to the sound waves detected by the microphone. The magneticfield created by the electromagnetic driving coil interacts with themagnetic field created by the magnet, creating a force which vibratesthe magnet and the malleus bone to which it is attached. To insure thatthe magnet is securely attached to the malleus bone, a pair of titaniumself tapping mini-screws are inserted through a hole in the magnet andinserted through a hole in the magnet and inserted into two man-mademicrocavities created in the malleus bone with the aid of a KTP 532laser. Once the screws are inserted into the malleus bone, they areallowed to osseo-integrate for a three month period. After this periodof time, the replaceable outer ear canal unit is put into use. The SmCO₅magnet would weigh about 30 to 35 mg and the distance between thismagnet and the external ear canal unit would be 3 to 5 mm.

Another variation of this system consists of placing the magnet encasedin a titanium dish anchored to the lateral aspect of the incus. Twoholes are made in the body of the incus, using the KTP 532 laser. Thetitanium extension of the dish is secured to the incus by two selftapping screws introduced through the previously made holes.

Another aspect of the present invention is drawn to a totally concealed,partially implantable hearing device having a replaceable outer earcanal unit having means for generating radio frequency waves responsiveto acoustic energy or sound waves that enter the ear and travel down theouter ear canal to the unit. Again, a microphone detects the sound wavesand, with the help of a battery and an electronic amplifier, transformsthe sound waves into amplified electrical signals. In this aspect,however, the amplified electrical signals are sent to an externalinduction coil or radio signal transmitting antenna to be converted intoamplitude modulation (AM) radio frequency waves that are transmitted toan internal induction coil implanted under the skin in the outer earcanal wall. An implanted electromagnetic driving coil, connected to theinternal induction coil, again creates a magnetic field that varies inresponse to the sound waves detected by the microphone. This magneticfield interacts with another magnetic field created by a magnet attachedto a bone in the ossicular chain in the ear. This interaction causes aforce which vibrates the magnet and the bone to which it is attached. Inone case, the bone to which the magnet is attached is the stapes; inanother case the magnet is attached to the incus; while in a third casethere is an electromagnetic-mechanical system having a very thin metaldiaphragm attached to a titanium coil spring secured to the incus body,using a self-tapping titanium screw introduced through a hole, KTP 532laser made. In another design the titanium spring coil is attached to acup-bumper which "sits" on the stapes head.

Still another aspect of the present invention is drawn to a partiallyconcealed, partially implantable hearing device having a replaceablehidden external unit adapted to be located externally and medially to anupper portion of a pinna of an ear, rather than being located inside theouter ear canal of the ear. A microphone detects the sound waves and,with the help of a battery, an electronic amplifier and an externalinduction coil, the sound waves are converted into amplitude modulation(AM) radio frequency type waves for transmission to an internalinduction coil implanted under the skin behind the ear. An implantedelectromagnetic driving coil, connected thereto, creates a magneticfield that varies in response to the sound waves detected by themicrophone. The magnetic field created by a magnet attached to a bone inthe ossicular chain in the ear interacts with the magnetic field createdby the electromagnetic driving coil, causing the magnet and the bone towhich it is attached to vibrate. Again, in one case, the bone is thestapes bone; in another case the bone is the incus; while in a thirdcase the electromagnetic-mechanical system mentioned above is employed.In order to remote control the in ear canal unit another unit handheld,pocket type, similar to a remote control television system would be usedfeaturing on and off and volume, up and down switches, activated byradio frequency transmission.

The various features of novelty which characterize the invention arepointed out with particularly in the claims annexed to and forming apart of this disclosure. For a better understanding of the presentinvention and the advantages attained by its use, reference is made tothe accompanying drawings and descriptive matter in which preferredembodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a coronal cut view of an ear which has received a firstembodiment of the invention in which the magnet has been secured to themalleus bone in the ossicular chain;

FIG. 2 shows a coronal cut view in which the magnet is secured to thebody of the incus in a titanium dish.

FIGS. 3 and 4 show detail of the titanium disc-magnet as shown in FIG. 2and how it is anchored to the body of the incus.

FIG. 5 shows a coronal cut view of an ear which has received a secondembodiment of the invention in which the magnet has been secured to thestapes bone in the ossicular chain, induction coils send/receive theradio frequency waves through the skin of the outer ear canal wall, andwhere the electromagnetic driving coil is attached to a supporting shaftinserted in the mastoid-attic cavity.

FIG. 6 shows a modified version of the third embodiment of FIG. 5 inwhich the intermediate structure is located in the posterior bony canal,closer to the outer ear canal wall of the ear.

FIGS. 7 and 8 show the magnet implanted onto the head of the stapes boneby means of an intermediate plastipore cup;

FIGS. 9 and 10 show a modified version of the embodiment of FIGS. 6, 9and 10 illustrating an electromagnetic-mechanical driving coil whichactivates a very thin metal membrane attached to an intermediate springcoil connected to a cup-bumper which "sits" on the stapes head.

FIGS. 11 and 12 show another version showing themastoidectomy-atticotomy surgical view presented when the intermediatestructure and electromagnetic driving coil are positioned in the attic,and a close-up view of the implanted magnet when secured to the body ofthe incus in the ossicular chain which is intact. A hole is made withthe laser and the magnet "T" extension is cemented into the incus.

FIGS. 13 and 14 show a modified version of the embodiment of FIGS. 11and 12. An electromagnetic-mechanical system in which an electromagneticcoil activates a diaphragm made out of a very thin (10 microns) metalmembrane attached to the body of the incus by means of a titaniumintermediate spring coil. A self tapping titanium screw secures theeyelet of the coil on the incus, through a laser made hole.

FIG. 15 depicts a behind the ear external unit which is secured inposition by two strong SmCO₅ magnets. By radio frequency the twoinduction coils transmit electric impulses. This unit is a substitute ofthe in the ear canal unit to be used by patients with less manualdexterity. This behind the ear unit may activate any of the drivingcoils previously described, connected to the ossicular chain by thedifferent embodiments. A modified version of this unit would be by meansof direct coupling with a percutaneous osseo-integrated titanium screw.Direct wiring from the amplifier to the electromagnetic coil in themiddle ear would then be used therefore eliminating the need fortranscutaneous radio transmission. The titanium screw abutment would bedirectly connected to the behind the ear unit. No need for the SmCO₅magnets to hold the unit would be required.

FIG. 16 shows a schematic electrical diagram of the partiallyimplantable hearing aid of the present invention utilizing the externaland internal inductions coils.

FIG. 17 shows a detailed electrical diagram of the amplifier andoscillator-modulator of the present invention (5 mega Hz).

FIG. 18 shows a comparison of frequency response for a piezoelectricversus electromagnetic system as measured by a laboratory model; and

FIG. 19 shows results of tests of the partially implantableelectromagnetic hearing aid which were performed in cats and in which a35 dB gain (average) was achieved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings generally, wherein like numerals designate thesame element throughout the several drawings, and to FIGS. 1 and 2 inparticular, there are shown cross-sectional views of an ear, generallyreferred to as 10, which has received the hearing device of the presentinvention.

The ear 10 is made up of an outer ear 12, a middle ear 14, and an innerear 16 (as best shown in FIG. 5). The outer ear 12 includes an auricleor pinna 18, and an outer ear canal 20. The pinna 18 collects acousticenergy or sound waves from the environment and directs them into theouter ear canal 20 which conveys the sound waves by air conduction to atympanic membrane or ear drum 22, which separates the outer ear 12 fromthe middle ear 14.

The middle ear 14 contains a series of three tiny interconnected bones:the malleus (hammer) 24; the incus (anvil) 26; and the stapes (stirrup)28. Collectively, these three bones are known as the ossicles or theossicular chain. The malleus 24 is attached to the tympanic membrane 22while the stapes 28, the last bone in the ossicular chain, is attachedto the oval window (inner ear) (not shown).

Sound waves that travel down the outer ear canal 20, strike the tympanicmembrane 22 and cause it to vibrate. The malleus 24, being connected tothe tympanic membrane 22, is thus also set into motion, along with theincus 26 and the stapes 28. These three bones in the ossicular chain actas a set of levers to amplify the tiny vibrations received by thetympanic membrane 22. By the time the vibrations are transmitted to theoval window (not shown) the pressure vibrations received by the tympanicmembrane 22 have been magnified by as much as 22 times. The stapesvibrates in turn, causing fluid in a spiral structure known as thecochlea 30 to move along its length. Very small hairlike cells (notshown) in the cochlea 30 are stimulated by the movement of fluid in thecochlea 30. There, hydraulic pressure displaces the inner ear fluid andmechanical energy in the hair cells is transformed into electricalimpulses which are transmitted to neural pathways and the hearing centerof the brain (temporal lobe), resulting in the perception of sound.

Referring now to FIG. 1, there is shown a first embodiment of thepresent invention, drawn to a totally concealed, partially implantablehearing device generally referred to as 32. The hearing aid 32 includesa replaceable outer ear canal unit 34 and a magnet 36. The outer earcanal unit 34 would be inserted into the outer ear canal 20 by means ofa forceps (not shown) similar to the type used in bronchoscopy forforeign body removal. The unit 34 is encased and hermetically sealed ina silicone mold for protection against corrosion from body fluids andfor ease of insertion into the outer ear canal 20. The size of the unit34 is generally adapted using an ear canal impression mold (not shown)to be closely received by the outer ear canal 20 without discomfort tothe wearer and may advantageously be cylindrical or oval in shape. Itmust conform to the shape of the outer ear canal 20. For individualswith narrow outer ear canals 20, canalplasties could be performed toallow accommodation of the unit 34.

The unit 34 receives acoustic energy or sound waves which are collectedby the pinna 18 and conveyed down the outer ear canal 20. The unit 34includes a microphone or transducer 38 for converting the acousticenergy or sound waves into electrical signals representative thereof; anamplifier for 40 for amplifying these electrical signals, a power supplyor battery 42 for providing electrical energy to the microphone 38 andamplifier 40; and an electromagnetic driving coil 44 for generating afirst magnetic field responsive to the amplified electrical signalsrepresentative of the sound waves received by the unit 34.

Advantageously, the microphone 38 can be an electret microphone, such asmanufactured by Knowlls Corporation. Typically, the microphone 38 wouldbe placed on the end of the unit 34 facing the ear or pinna 18associated with the outer ear canal 20 which received the unit 34. Theamplifier 40 may advantageously be a microchip unit. The battery 42 mayadvantageously be of the nickel-cadmium or manganese/dioxide lithiumcell type, chosen for their long life to minimize insertion andreplacement of the unit 34 into the outer ear canal 20. Since the unit34 is easily insertable and replaceable by means of the forceps (notshown) mentioned earlier, repairs of the unit 34 or changing of thebattery 42, when necessary, can easily be achieved. If desired, a spareunit 34 could be provided to a patient to be worn in the interim shouldrepairs to the unit 34 be necessary, to eliminate "down time".

The electromagnetic driving coil 44 would typically have a ferrite-alloycore of dimensions of 9 mm×2 mm wrapped with approximately 3,000 turnsof AWG (American Wire Gauge) #55 copper wire, resulting in a highlyefficient coil. AWG #55 copper wire has a nominal outside diameter ofless than 1.8 mils (1 mil=0.001 inch=0.025 mm). Generally, theelectromagnetic driving coil 44 would be placed on an end of the unit 34opposite the end having the microphone 38.

The magnet 36 is securely attached to the malleus bone 24 in theossicular chain of the ear 10, thus eliminating thespeaker/earphone/receiver (not shown) of conventional hearing aids.While others (Goode, Bojrab, et al) tried this system in humanvolunteers with favorable results, difficulties have been encountered inadequately securing the magnet onto the tympanic membrane 22. Differentadhesives have been used with poor results: the magnet becomes dislodgedfrom the tympanic membrane 22 and the system malfunctions. In contrast,the present invention circumvents this problem by securing the magnet 36to the handle of the malleus 24 by means of two mini cavities 46therein. A KTP 532 laser (not shown) would be used to create the twomini cavities 46, which would then be the receptacle for two titanium,self tapping screws 48. A titanium abutment 49 is inserted through holesdrilled in the magnet disc advantageously, a rare earth, samarium cobaltSmCO₅ magnet and screwed with threads situated in the head of thetitanium screws 48 which has been previously inserted in the malleus 24.A lapse of 3 months from the time of insertion of the screws 48 to theplacement of the abutment 49 is necessary for biointegration.Biointegration takes place under sterile conditions created as follows.A small flap of ear drum on the malleus handle is reflected exposingbare bone. The minicavities 46 are created with the laser and theself-tapping screws 48 are applied. The flap of ear drum covers the headof the screws 48. Healing takes place, and after 3 months the head ofthe screws 48 are exteriorized and the titanium abutment 49 with thesamarium cobalt magnet 36 is secured to the head of the screws 48. Thenthe outer ear canal unit 34 would be inserted in the outer canal 20.

The location of the end of the electromagnetic driving coil 44 withrespect to the end of the magnet 36 is critical for optimum efficiency,since the degree of interaction between the first magnetic field createdby the electromagnetic driving coil 44 and the magnet 36 is inverselyproportional to the cube of the distance there between. For example, ifthe distance between these two elements 36 and 44 is doubled from about5 mm to 10 mm, the force from the electromagnetic driving coil 44 actingon the magnet 36 is reduced eightfold. Preferably, the distance betweenthe magnet 36 and the electromagnetic driving coil 44 should beapproximately 3 to 5 mm. In practice, a patient using the hearing aid 34would be trained to insert the unit 34 with the forceps (not shown) intothe outer ear canal 20 and, when noticing optimum hearing improvement,would remove the forceps (not shown) without disturbing the position ofthe unit 34. Removal of the unit 34, for repairs or replacement of thebattery 42 would be accomplished by the reverse procedure.

Referring to FIGS. 2, 3, and 4, it shows another version of FIG. 1whereby the magnet 36 in a variant form 37 is secured to the body of theincus in a titanium dish 51. The distance between ear drum and unit 34would be to 3 mm. Magnets 66 and 68 (SmCO₅) secure unit 34 in each earcanal 20. The incus 26 would vibrate through the interaction of magneticfields of coil 44 and magnet (SmCO₅) 37 in a titanium dish 51 secured tothe incus body with self tapping titanium screws (53) introduced inlaser (not shown) created cavities 55.

Referring to FIG. 5, there is shown a second embodiment of the presentinvention, drawn to a totally concealed, partially implantable hearingdevice generally referred to as 50. The hearing device 50 includes areplaceable outer ear canal unit 52, a magnet 54 securely attached to alocation on a bone in the ossicular chain of the ear 10, and supportingshaft 56. The supporting shaft 56 is shown in FIG. 5 as being located ina mastoid-attic cavity 58; other locations are possible as will bediscussed later.

The outer ear canal unit 52 receives acoustic energy or sound wavescollected by the pinna 18 and conveyed down the outer ear canal 20, muchin the fashion of the previously discussed outer ear canal unit 34.Similarly, the unit 52 includes a microphone or transducer 60, anamplifier 62, and a power supply battery 64 whose relative positions,structure and functions are substantially identical to those of theirconterparts 38, 40 and 42, respectively, in the unit 34. The unit 52would also be encased and hermetically sealed in a silicone mold forease of insertion and removal and for protection against corrosion frombody fluids. However, in contrast to the unit 34, the outer ear canalunit 52 also contains an external induction coil or radio frequency wavesignal transmitting antenna 66. The microphone 60, the amplifier 62 andthe battery 64 receive, amplify and convert the sound waves received bythe unit 52 into electrical signals representative thereof. Theseelectrical signals are then sent to the external induction coil 66 whichgenerates amplitude modulation (AM) radio frequency waves reponsive tothe acoustic energy or sound waves received by the unit 52.

Implanted under the skin of the wall of the outer ear canal 20 is aninternal induction coil or radio frequency wave signal receiving antenna68. Implantation of the internal induction coil 68 would typically beperformed through a mastoidectomy approach, being laterally lodged inthe posterior bony wall of the outer ear canal 20. The externalinduction coil 66 transcutaneously transmits the radio frequency waves,advantageously amplitude modulation (AM) radio frequency waves,representative of the sound waves received by the unit 52, to theinternal induction coil 68. Wires 70 would interconnect the internalinduction coil 68 to an electromagnetic driving coil 72 located adjacentto but spaced away from the magnet 54, which again is preferably a rareearth, samarium cobalt magnet. The electromagnetic driving coil 72 issupported by the supporting shaft 56. The electromagnetic driving coil72 thus creates a first magnetic field, responsive to the sound waves oracoustic energy received by the unit 52, that interacts with themagnetic field created by the magnet 54, causing it and the bone in theossicular chain to which it is attached to vibrate. As shown in FIG. 5,the bone in the ossicular chain could be a stapes bone 74; other bonesin the ossicular chain are equally likely candidates.

The outer ear canal unit 52 would be inserted or removed from the outerear canal 20 in a similar manner as described for the unit 34. However,to ensure that the unit's 52 external induction coil 66 is inapproximate alignment with its counterpart internal induction coil 68,an external positioning magnet 76 is placed in the outer ear canal unit52 near the outer surface thereof, while an internal positioning magnet78 is implanted under the skin in the outer ear canal wall 20. Theexternal and internal positioning magnets 76, 78, preferably also of therare earth, samarium cobalt type, have magnetic fields that interactwith each other, resulting in a holding force that holds the unit 52 ata selected position in the outer ear canal wall 20. Magnets 76 and 78could also be used, in the first embodiment, to secure the outer earcanal unit 34 in the outer ear canal wall 20, if desired. The positionof the external induction coil 66 and the external positioning magnet 76on the unit 52 are chosen so that they are substantially adjacent theircounterparts 68 and 78, respectively, implanted under the skin of theouter ear canal wall 20. Similarly, the microphone 60 is also arrangedwith respect to the external positioning magnet 76 and externalinduction coil 66 so that it faces the pinna 18 associated with theouter ear canal 20 which receives the unit 52 when the positioningmagnets 76, 78 and the induction coils 66, 68 are substantially adjacenteach other.

The electromagnet driving coil 72 must be placed at a precise distanceaway from the adjacent magnet 54. Preferably, this distance isapproximately 2 mm. In this embodiment, the electromagnet driving coil72 would typically have a ferrite-alloy core of dimensions 7 mm×2 mm,wrapped with approximately 3,000 turns of AWG #55 copper wire.

The supporting shaft 56 is used to secure and position theelectromagnetic driving coil 72 with respect to the magnet 54. In apreferred embodiment, the supporting shaft 56, is an L-shaped, titaniumplate shaft capable of telescoping to increase or decrease its length soas to permit selection of the optimal coupling distance between theelectromagnetic driving coil 72 and the magnet 54 (not shown). The endof the structure 56 opposite the end holding the coil 72 would besecured to the temporal bone structure by means of a plate 80 and screws82, also preferably made of titanium. A hanger 84 having a set screw 86provides an additional support and allows for fixation of the length ofthe telescoping intermediate structure 56.

FIG. 6 shows a modified version of FIG. 5 in which the supporting shaft56 is located in the posterior bony canal 88 closer to the outer earcanal wall 20 of the ear 10.

Referring to FIGS. 7 and 8, there is shown two close-up views of thestapes bone 74 to which the magnet 54 has been attached. Anintermediate, biocompatible, plastipore cup 90 would preferably be usedto glue the magnet 54 to the head of the stapes bone 74, rather thangluing the magnet 54 directly to the stapes 74. This arrangementfacilitates, should the need arise, removal of the magnet 54 off of thehead of the stapes 74 by means of simply cutting off the plastipore cup90.

FIGS. 9 and 10 depict a modified version of FIGS. 5 and 6 whereby anelectromagnetic-mechanical system 94 is selected. A ferrite-alloy iswrapped with 1300 turns of #45 copper wire 96. When energized, itactivates the thin metal membrane 98 attached to a titanium spring coil100 welded to a cup-bumper 102 which "sits" on the stapes head. Theappropriate stiffness of the spring is critical to good function.

Referring now to FIGS. 11 and 12, there is shown another modifiedversion of FIGS. 5 and 6 showing, respectively, the surgical viewpresented when the intermediate structure and its attachedelectromagnetic driving coil 72 are positioned in the attic, and acloseup view of the implanted magnet 54 secured to the body of the incusbone 26. In general, it is advantageous to attach the magnet 54 directlyto the head of the stapes 74 (via the intermediate plastipore cup 90)since less driving force is required to vibrate the stapes 74, resultingin reduced power consumption of the unit 52. However, in sensorineuralhearing loss, in order to avoid an iatrogenic conductive hearing loss,it is desirable not to disconnect the ossicular chain. In such cases,the alternative approach shown in FIGS. 11 and 12 would be desirable.The magnet 54 is attached to the body of the incus bone 26, by means ofa T-shaped pin 92 inserted and cemented with methyl methacrylate into aminicavity 46 placed into the incus bone 26. A laser (not shown) couldagain be used to create the minicavity 46 as described before. Thetitanium screw technique described earlier could also be applied tosecure the magnet 54.

Referring now to FIGS. 13 and 14, there is shown anelectromagnetic-mechanical system generally referred to as 94, in whichan electromagnetic coil 96 activates a diaphragm 98 made out of a verythin (10 microns) metal membrane. Attached to the diaphragm 98 is afirst end of a titanium spring coil 100; the attachement can be bysoldering or other suitable means. The stiffness of the spring coil iscritical in order to avoid a shock absorber effect. A hole 102 is againcreated by means of a laser (not shown) which would receive aself-tapping titanium screw 104, advantageously 3 mm long by 0.75 mm indiameter. A second end of the spring coil 100 is secured to the screw104, thus coupling the diaphragm 98 to the body of the incus 26. Equallysuited for the second or third (infra) embodiments of the invention, theelectromagnetic-mechanical system 94 would be attached to the supportingshaft 56, and would vibrate the incus 26 by means of the diaphragm 98and spring coil 100 in response to electrical signals, transmitted alongwires 70, representative of received acoustic energy or sound wavesdetected by a microphone of the present invention.

Referring now to FIG. 15, there is shown a third embodiment of thepresent invention, drawn to a partially concealed, partially implantedhearing aid generally referred to as 108. The hearing aid 108 includes areplaceable, partially hidden external unit 108, the magnet 60 securelyattached to a bone in the ossicular chain, and the supporting shaft 56.

The external unit 110 is adapted to be located externally and mediallyto an upper portion of the pinna 18. The external unit 110 includes themicrophone or transducer 60, the amplifier 62 and the power supply orbattery 64, whose relative positions, structure, and functions aresubstantially identical to those shown and discussed in the secondaforesaid embodiment. Since the external unit 110 is not inserted intothe outer ear canal wall 20, it need not be encased and hermeticallysealed in the silicone mold required for the previous embodiments.

To hold the external unit 110 at the selected external position locatedmedially near the upper portion of the pinna 18 of the ear 10, externaland internal positioning magnets 76, 78, respectively, are againprovided. In this application, however, the internal positioning magnet78 is implanted under the retroauricular skin behind the pinna 18 of theear 10. The internal positioning magnet 78 interacts with and holds theexternal positioning magnet 76 and its attached external unit 110 at theselected position. If necessary, a transparent hook (not shown) attachedto external unit 110 and hanging over the pinna 18 could be used tofurther stabilize the external unit 110 behind the pinna 18.

In operation, the microphone 60 of the external unit 110 receivesacoustic energy or sound waves from the environment. The microphone 60,the amplifier 62 and the battery 64 receive, amplify and convert thesound waves received by the external unit 110 into electrical signalsrepresentative thereof as described earlier. These electrical signalsare then sent to the external induction coil 66 which generates radiofrequency waves responsive to the acoustic energy or sound wavesreceived by the microphone 60 of the external unit 110 as describedearlier.

The internal induction coil 68 is implanted under the retroauricularskin behind the pinna 18 of the ear 10 for transcutaneously receivingthe radio frequency waves, advantageously amplitude modulation (AM)radio frequency waves, broadcast by the external induction coil 66. Thepositions of the external and internal induction coils 66, 68, externaland internal positioning magnets 76, 78 and the microphone 60 is nearthe upper portion of the pinna 18 of the ear when the external unit isin place. This placement of the microphone 60 gives the best exposure toallow optimum sound reception from the environment.

Wires 70 interconnect the internal induction coil 68 to theelectromagnetic driving coil 72 supported by the intermediate structure.The electromagnetic driving coil 72 creates a first magnetic field,responsive to the sound waves or acoustic energy received by theexternal unit 110, that interacts with the magnetic field of the magnet54, causing it and the bone in the ossicular chain to which it isattached to vibrate. These vibrations are transmitted to the cochlea 30,leading to the eventual perception of sound in the hearing center of thebrain.

The electromagnetic driving coil 72 would be substantially identical tothat used in the aforementioned second embodiment, having aferrite-alloy core of specified dimensions wrapped with approximately2000 turns of AWG #45 copper wire. The intermediate structure againfunctions to position and secure the electromagnetic driving coil 72 atthe preferred 2 mm distance from the magnet 54. Telescoping and fixationfeatures of the intermediate structure allow for precise location of theelectromagnetic driving coil 72, as well as for differences in anatomyand firm fixation.

The material for the magnet 54 and the positioning magnets 76, 78 maypreferably be a rare earth, samarium cobalt material as before. Theplastipore cup 90 would preferably again be used if the magnet 54 is tobe attached to the head of the stapes bone 74; of course, attachmentinstead to the incus bone 26 may also be accomplished as previouslydescribed to address cases of sensorineural hearing loss, as well as theelectromagnetic-mechanical system coupled with the stapes head.

FIG. 16 shows a schematic electrical diagram of the partiallyimplantable hearing aid of the present invention, applicable to thetotally concealed, partially implanted embodiment 50 and the partiallyconcealed, partially implanted embodiment 108. In the first embodiment,the RF transmitters and receivers would, of course, be omitted.

FIG. 17 shows a detailed electrical diagram of the amplifier 40, 62 andoscillator-modular of the present invention. As indicated therein, theinput to the circuit would come from the microphone 38, 60 and wouldconvert the received acoustic energy or sound waves into electricalsignals representative thereof.

The selection of an electromagnetic driving coil 72 for the presentinvention was a calculated decision based upon laboratory experimentsdesigned to specify the microvibrational characteristics of themagnet-weighed ossicles of fresh cat and human temporal bones. The goalin this experiment was to determine the optimal type of vibratorystimulator for implantation. Specifically, it was necessary to deterinewhether an electromagnetic or a piezoelectric circuit would produce asignificantly different frequency response of stapedial vibration. Thepiezoelectric device tested in our laboratory showed a peak frequencyresponse of 1.9 KHz, where the electromagnetic system was characterizedby a uniform flat and broader frequency response, which will be observedin reference to FIG. 18. While the normal human ear has perception ofsound in the 20-20,000 Hz range, the critical speech range is 500-3000Hz. Based on this data, the electromagnetic principle was used for thepresent invention.

EXPERIMENTAL TESTS

Two versions of middle ear stimulator using the electromagneticprinciple were developed: (1) miniaturized driving coil (2.25 mmdiameter) by 13.5 mm long (1300 turns of AWG #45 copper wire) and acup-like samarium cobalt magnet (SmCO₅); (2) special fine diaphragm ormetal membrane, 6 mm in diameter excited by electromagnetic components.A 5-0 stainless steel wire was soldered to the center of the metalmembrane to be crimped to the ossicles. For comparison, a piezoelectricstimulator of bimorph design attached to the head of the stapes was alsoevaluated in the laboratory. The electromagnetic coil with the magnet onthe head of the stapes was found overall to be more efficient and havemore advantages. The systems were tested in fresh human cadavers andfresh cat cadavers.

Ossicular microvibration below one micron was measured using anoptoelectronic laser beam system. The displacement of the stapes orincus in the middle ear of fresh cat cadaver (less than 8 hours afterdeath) was measured in response to the activation of the different typesof implantable middle ear hearing aid. Also, the characteristics of thetwo types of electromagnetic stimulators and the piezoelectricstimulator driving the isolated stapes of anesthetized cats werecompared. The electromagnetic stimulator has a more uniform flat andbroader frequency response and does not require direct contact with thestapes. The results were similar to the data shown in FIG. 18.

For these reasons, the electromagnetic miniaturized driving coil wasselected after the preliminary engineering testing to be used in acuteanimal experiments. Seven anesthetized adult cats were used. Thepreoperative hearing thresholds to 100 micro sec rarefaction clicks wererecorded using a Nicolet Compact IV electrodiagnostic unit.

The skin and muscles overlying the cat's attic and bulla tympani wereincised and retracted through a posterior auricular approach. With theaid of the Zeiss operating microscope, an atticotomy was performed usingan electric drill with cutting burs and bone curettes. The incus wasthen removed and the hearing again tested after the atticotomy defectwas sealed with bone wax. A small cylindrical SmCO₅ magnet (27 mg),cup-shaped was placed over the head of the stapes. A central portion hadbeen drilled out from one end of the magnet so that the head of thestapes could fit into the magnet.

Cyanoacrylate was used to cement the magnet to the stapes usingnonmagnetic instruments. Care was taken to keep the middle ear dry andto assure that the magnet was able to vibrate freely and did not abutany other part of the middle ear cavity, the malleus, or the facialnerve.

A silicone-coated ferrite core transducer coil (13.5 mm length×2.25 mmdiameter) with AWG #45 copper wire (1300 turns) was placed approximately2 mm from the stapes magnet assembly and held into a fixed position withexternal devices. The cat's head was immobilized in a vise-like device.The resistance of the coil was 118.3 Ohms.

1. ACOUSTIC MEASUREMENTS

Auditory brainstem potentials (ABP) were elicited and recordedpreoperatively and postoperatively in the acute experimental animal(cat) using a Nicolet Compact IV electrodiagnostic system. Theexperimental measurement protocol required three different transducerinterfaces: earphone/ear drum; earphone/microphone and coil/magnet asdescribed below. An open (free-field system) was thus employed withintensities monitored on an oscilloscope at the level of the earphone bya probe microphone.

During ear drum stimulation, probe microphone measurements into the earcanal to within 5 mm of the ear drum showed a signal enhancement of nogreater than 3 dB referenced to the output of the earphone and thiscould theoretically be offset by changing the earphone/microphoneinterface distance. However, the coil/magnet interface distance was morecritical as variations of 1 mm could produce a threshold differential ofas great as 5 to 10 dB. Therefore, signal intensities were reported inincrements of no less than 5 dB to offset any uncontrolled measurementerror incurred by the changing transducer interface distance.

While the anesthetized animal was secured in the stabilizing frame: (1)the TDH39P shielded earphone was placed at 2-3 cm from the ear drum orat 1 cm from the microphone of the telemetry unit or (2) theelectromagnetic driving coil was placed at 2 mm from the stapedialmagnet. Stimuli consisted of 100 sec. monopolar square pulses at a rateof 22.3 per second delivered either as acoustic click stimuli by theearphone or as direct current pulses to the electromagnetic drivingcoil. Intensities were measured from the coil voltage and current usingan oscilloscope. All recordings were made in the free-field environment.

The EEG activity was recorded in a single channel bipolar derivationfrom Grass platinum subdermic needle electrodes applied in a midlinemontage: midline central scalp, neck with supraorbital site as ground.This montage remained constant for all recordings and was selected forits equidistance to either ear and for its remote location from thesurgical site, minimizing interference artifact observed when theelectromagnetic driving coil was in close proximity to the activerecording site.

The auditory brainstem evoked response was averaged over several hundredsweeps to enhance the signal-to-noise ratio. The frequency response ofthe amplifier was set at 100 to 3000 Hz pass band and the averager wasgated on during the 10 msec. following each stimulus presentation.

The response emerged as the classic far-field potential consisting offive characteristic peaks at higher stimulus intensities with a robustWave IV noted in the species persisting at lower intensity levels.

In each experimental condition, a reference intensity presentationseries was established and replicated at 90 dBSPL. Successive runs werethen performed at 5 dB decrements until a minimal response level (ABPthreshold) was bracketed and replicated. Each averaged response wasanalyzed for morphology and replicability.

Each animal was evaluated in one preoperative and three postoperativeconditions.

Preoperative: With an earphone at the test ear and contralateral broadband masking delivered via an insert earphone, ABP was obtained to clickstimuli at the reference level (90 dBSPL) which is extrapolated to 60dBHL. ABP thresholds were established on a 5 dB increment scale andserved as the threshold value against which postoperative thresholdswere compared.

Postoperative #1: ABP thresholds were reestablished to adjust forchanges incurred by the operative technique, (i.e., drilling, openingthe bulla tympani, disruption the ossicular chain). The operative sitewas cleared of blood and sealed with bone wax prior to testing. As theoperative technique involved removal of the incus, substantialinteraural threshold differences were created, necessitating high levelsof contralateral broadband masking to limit participation of the nontestear. Masking was demonstrated to be effective provided that stimulusintensity did not exceed 100 dBSPL (70 dBHL).

Postoperative #2: The monopolar square wave current pulse from theNicolet system was applied to the driving coil mounted to a stabilizingframe and positioned at 2 mm distance from the SmCO₅ magnet glued to thestapes head. ABP thresholds were then reestablished on a negative dBscale relative to the reference coil voltage and current.

Postoperative #3: In this experiment, click stimuli were then transducedby the TDH39P earphone now mounted at a distance of 1 cm to the electretcondenser microphone of the telemetric radio frequency coil system.Threshold measures were again performed as described in the preoperativecondition.

2. EXPERIMENTAL RESULTS

FIG. 19 depicts the ABP thresholds for each experimental condition inthe seven acute animal experiments.

In the preoperative baseline condition, the mean ABP click thresholds indecibels sound pressure level was 50.71 dBSPL (S.D.=6.7) with a 20 dBrange of values from a minimum of 40 dBSPL to a maximum of 60 dBSPLEquivalent thresholds in hearing level are 30 dB less than the soundpressure values, postoperatively, with the incus removed and theatticotomy defect sealed with bone wax, mean click threshold increasedto 94.28 dBSPL (S.D.=5.34), ranging from 90 to 105 dBSPL.

In the second postoperative condition, ABP thresholds were reassessed inorder to evaluate the coil/magnet interface. As described above, thismeasure was performed on a different scale using pulsed direct current(DC) generated by the Nicolet system with 50 mV, 0.3 mA as a referencelevel: 0 dB. This is the result of driving the coil with the Nicoletoutput set at "90 dBSPL". Coil induced thresholds ranged from -40 dB to-20 dB with a mean value of -27.14 dB (S.D.=6.36).

Six of the seven cat subjects were included in the third postoperativeauditory measurement. In this condition, ABP click thresholds werereestablished ranging from 50 to 70 dBSPL with a mean threshold of 60dBSPL (S.D.=7.07).

Implant gain was considered as the amount of threshold improvementachieved for each subject by means of the implanted telemetric device ascompared to the baseline thresholds obtained in the surgically-alteredcondition, incus removed (postoperative 1). Thus, implant gain value isexpressed in decibels referenced to the postoperative 1 condition. Themean "implant gain" was 35 dB (S.D.-4.47) with values ranging from 30 to40 dB of gain.

A paired test comparing the differences in means between the surgicallyaltered condition (postoperative #1) and the implanted condition(postoperative #3) was significant (t=19.17; df=5; p<0.001) indicatingthat the observed improvements in threshold with the implanted devicecould not be attributed to sampling error or other chance factors. Theexperimental data, particularly the significant improvement noted withthe telemetric circuit in place, supports the original researchobjectives: (1) to provide sufficient acoustic gain, and (2) minimalpower consumption of the implant. A mean acoustic gain of 35 dB wasachieved with the telemetry unit and this can be further increased byproviding additional amplification. The external unit can very well bebuilt with a more powerful adjustable amplifier which can be controlledby the user.

The power consumption of the implanted portion of the device wasefficient, consuming only 15 microwatts at 0 dB which is 27.14 decibels(mean value) above the threshold measured in this condition. This smallpower requirement made possible the design of the described telemetricsystem. The estimated power consumption of the external telemetry unitwas 2.4 milliwatts (4 V, 0.6 mA). As this represents the first prototypeunit, additional technological refinements in progress can be expectedto decrease power consumption by a factor of three (1.3 V, 0.6 mA, 0.8milliwatts).

This device appears to compare favorably to a medium power hearing aidwith respect to acoustic gain and power requirements. With the presentprototype, a 40 mA-hour battery can last for two weeks on an eight hourper day usage basis. With improved electronics, the battery life can beincreased threefold. Although discrete frequency ABP thresholds were notmeasured in the live animal, our optoelectronic laboratory data shows abroad, flat frequency response from 100 to 5000 Hz (see FIG. 18). Thistype of frequency response is expected to provide good sound fidelityand with the added telemetry unit, can be further modified (shaped) tothe specific needs of the patient, as in the conventional hearing aid.

The energy conversion system of the present invention is very efficient,due to its design. Acoustic energy picked up by the microphone istransformed into an electrical signal which is amplified and delivereddirectly to the transmitting (external) antenna, avoiding the need foracoustic energy conversion typical of the conventional hearing aid. Theconventional hearing aid requires a second conversion of energy(electrical to acoustic) by the speaker. The acoustic energy deliveredto the ear drum must be transferred through air molecules which, inturn, leads to a further depletion of energy due to impedance mismatchesand conduction losses. Not only does the elimination of a speaker leadto a better conversion of energy in the system, but it also avoids thewell-known problem of feedback.

The electronics of the implanted portion of the system are completelypassive, simple in design, and the components are very inexpensive. Theycontain no transistors. They are composed of a coil, two diodes, onecapacitor, and a driving electromagnetic coil with associated wiring.This implanted system requires no battery for operation. It is designedto be hermetically sealed and silicone coated. The components shouldlast indefinitely, requiring no revision surgery for electronicmalfunction. If there is a need for a battery, reoperations are notnecessary for battery change. Hermetic sealing avoids corrosiveinteractions between the hardware and body fluids. The electromagneticforces are transmitted to the ossicular chain on a contactless basis,therefore avoiding wear and tear of the ossicular chain.

The several embodiments can be adapted to the specific needs of thepatient. Patients with motivation and good manual dexterity, requiredfor insertion and care, can utilize the embodiments employing the outerear canal units 32, 52, and variations thereof. Older patients,especially those with limited manual dexterity would be candidates forthe miniaturized partially hidden, partially implanted hearing aidembodiment of FIG. 15, and variations thereof. Either of thesevariations provides simplicity in electronics and excellent cosmeticadvantages. Should the outer ear canal or external units 32 and 52,respectively, malfunction, there would be no "down time" as the patientcan replace it immediately with a spare unit.

While in accordance with provisions of the statutes there areillustrated and described herein specific embodiments of the invention,those skilled in the art will understand that changes may be made in theform of the invention covered by the following claims, and that certainfeatures of the invention may sometimes be used to advantage without acorresponding use of the other features.

I claim:
 1. A partially implantable hearing device, comprising:areplaceable outer ear canal unit, having means for generating radiofrequency waves responsive to acoustic energy received by the unit, andadapted to be located inside an outer ear canal of an ear; means forholding said replaceable outer ear canal unit in a selected position inthe outer ear canal; an implanted means for generating a first magneticfield responsive to said radio frequency waves, wherein said means forgenerating the first magnetic field comprises an internal induction coilimplanted under the skin in the outer ear canal wall fortranscutaneously receiving said radio frequency waves from said radiofrequency waves generating means, an electromagnetic driving coilconnected to said internal induction coil for generating said firstmagnetic field responsive to said radio frequency waves, and means forpositioning said electromagnetic driving coil adjacent to and at adistance from an implanted magnet securely attached to the location onthe bone in the ossicular chain in the ear; the implanted magnet havinga second magnetic field located adjacent to said electromagnetic drivingcoil at a distance sufficient to permit the first and second magneticfield to interact with each other to cause the magnet to vibrate in amanner responsive to the acoustic energy received by the unit; and meansfor securely attaching the implanted magnet to a location on a bone inthe ossicular chain in the ear.
 2. The hearing device of claim 1,wherein the means for generating the radio frequency waves responsive toacoustic energy received by the unit comprises:means for converting theacoustic energy received by the unit into electrical signalsrepresentative thereof; means for amplifying the electrical signals;means for providing electrical energy to the converting and amplifyingmeans; and an external induction coil, connected to said amplifyingmeans, for generating the radio frequency waves responsive to theacoustic energy received by the unit.
 3. The hearing device of claim 2,wherein the means for converting the acoustic energy received by theunit into electrical signals representative thereof comprises electretmicrophone.
 4. The hearing device of claim 3, wherein the electretmicrophone is located facing the ear associated with the outer ear canalwhich receives the unit.
 5. The hearing aid of claim 2, wherein themeans for holding the replaceable outer ear canal unit at the selectedposition in the outer ear canal comprises:an external positioningmagnet, located in the replaceable outer ear canal unit near an outersurface thereof; and an internal positioning magnet, implanted under theskin in the outer ear canal wall, for interacting with and holding theexternal positioning magnet and its attached unit at the selectedposition in the outer ear canal.
 6. The hearing device of claim 5,wherein the external induction coil is substantially adjacent to theinternal induction coil implanted under the skin in the outer ear canalwall when the internal and external positioning magnets are holding theunit at the selected position in the outer ear canal wall.
 7. Thehearing device of claim 6, wherein the internal and external positioningmagnets are the rare earth samarium cobalt magnets.
 8. The hearingdevice of claim 1, wherein the location on the bone in the ossicularchain in the ear is a head of a stapes bone.
 9. The hearing device ofclaim 8, wherein the means for positioning the electromagnetic drivingcoil adjacent to the magnet comprises:a titanium, L-shaped platesupporting shaft implanted and secured at one end thereof to theelectromagnetic driving coil; and a hanger, located intermediate theends of the L-shaped plate shaft and secured to the temporal bonestructure.
 10. The hearing device of claim 9, wherein the L-shaped plateshaft has means for telescoping to increase or decrease its length topermit selection of the optimal coupling distance between theelectromagnetic driving coil and the implanted magnet attached to thehead of the stapes.
 11. The hearing device of claim 8, wherein the meansfor securely attaching the implanted magnet to the head of the stapesbone in the ossicular chain in the ear comprises:a biocompatible,plastipore cup glued at one end to the head of the stapes bone and gluedat the other end to the implanted magnet.
 12. The hearing device ofclaim 1, wherein the electromagnetic driving coil includes aferrite-alloy core wrapped with approximately 2000 turns of AWG #45copper wire.
 13. The hearing device of claim 12, wherein the distancebetween the electromagnetic driving coil and the implanted magnet isapproximately 2 millimeters.
 14. The hearing device of claim 13, whereinthe implanted magnet is a rare earth samarium cobalt magnet.
 15. Thehearing device of claim 1, wherein the bone in the ossicular chain inthe ear is the incus bone, where said incus bone further includes aman-made minicavity therein, and wherein the means for securelyattaching the implanted magnet to the incus bone is a titanium dishconnected to a T shaped titanium pin and cemented to the body of theincus.
 16. The hearing device of claim 1, wherein the radio frequencywaves are of the amplitude modulation (AM) radio frequency type.
 17. Thehearing device of claim 11, wherein the bone in the ossicular chain inthe ear is the incus bone, wherein said securely attaching meansincludes means for vibrating said incus bone in the ear in a mannerresponsive to the acoustic energy received by the unit.
 18. The hearingdevice of claim 17 further comprises a remote control unit for saidvibrating means, wherein said remote control unit having remote volumecontrol and remote power on and off control.
 19. A partially implantablehearing device, comprising:a replaceable hidden external unit, havingmeans for generating radio frequency waves responsive to acoustic energyreceived by the unit, and adapted to be located externally and mediallyto an upper portion of a pinna of an ear; means for holding saidreplaceable hidden external unit in a selected external position locatedmedically near the upper portion of the pinna of the ear; an implantedmeans for generating a first magnetic field responsive to said radiofrequency waves, wherein said means for generating the first magneticfield comprises an internal induction coil implanted under aretroauricular skin behind the ear for transcutaneously receiving saidradio frequency waves from said radio frequency waves generating means,an electromagnetic driving coil connected to said internal inductioncoil for generating said first magnetic field responsive to said radiofrequency waves, and means for positioning said electromagnetic drivingcoil adjacent to and at a distance from an implanted magnet securelyattached to the location on the bone in the ossicular chain in the ear;the implanted magnet, having a second magnetic field, located adjacentto said electromagnetic driving coil at a distance sufficient to permitthe first and second magnetic field to interact with each other to causethe magnet to vibrate in a manner responsive to the acoustic energyreceived by the unit; and means for securely attaching the implantedmagnet to a location on a bone in the ossicular chain in the ear. 20.The hearing device of claim 19, wherein the bone in the ossicular chainin the ear is the incus bone, wherein said securely attaching meansincludes means for vibrating said incus bone in the ear in a mannerresponsive to the acoustic energy received by the unit.